An engine is a machine capable of transforming other forms of energy into mechanical energy, and includes an internal combustion engine (gasoline engine, etc.), an external combustion engine (Stirling engine, steam engine, etc.), a motor, etc. For example, the internal combustion engine usually converts chemical energy into mechanical energy. The engine is suitable for power generating units, and may refer to an entire machine including the power units (such as gasoline engine and aero-engine).